The invention relates to a film scanner comprising a device for scanning sprocket holes.
In film scanners, the sprocket holes of a film are often optically scanned for deriving correction signals to control the transport speed or the frame position. For example, U.S. Pat. No. 4,855,836 discloses a film scanner in which a further arrangement for optically scanning the sprocket holes of the film is arranged proximate to an arrangement for optically scanning the film frames. In this film scanner, the arrangement for optically scanning the sprocket holes comprises both a light source for incident light illumination of the sprocket holes and an optical scanner for scanning the sprocket holes. The film is guided by means of a roll having guidance pins on its sides.
Ideally, the sprocket holes which were used in the pick-up camera for positioning the film frame should be scanned when scanning sprocket holes. In the majority of film material to be scanned, this is the pair of sprocket holes preceding the film frame and a generally denoted as Mitchell holes. Since the Mitchell holes are particularly very proximate to the film frame to be scanned, a direct scanning of the Mitchell holes has special difficulties. Frequently, there is no place left to provide an illumination source or a camera for scanning the Mitchell holes, because it is exactly in this area where the film frame is guided by guiding elements for mechanically improving the frame position. Arranging illumination sources and sprocket hole scanners at this position may also be obstructed by the film scanning head which is used for scanning the film frame.